1. Field of the Invention
The present invention relates to improvements in the structure of a temperature-sensing fan fluid coupling which permits the engine fan of an automobile to be rotated to automatically supply more or less cooling air according to the operating conditions of the engine at all times.
2. Description of the Prior Art
A typical fan fluid coupling of this kind is shown in FIG. 4, where a round hole 14' is formed in a partition plate 14 to control the outflow of oil. A resilient valve member 15 is mounted in the coupling and takes the form of a flat sheet. When temperature varies, a temperature-sensing device (not shown), such as a thermostat, mounted outside deforms, and the valve member 15 interlocks with a rodlike link member (not shown) in response to the deformation. At this time, the flat front end portion of the valve member 15 moves forward or rearward to directly close or open the hole 14'. The characteristic of the coupling is indicated by curve (B) of FIG. 5.
This prior art fan fluid coupling is unable to sufficiently control the outflow of oil, because the hole 14' is directly closed or opened by the flat front end portion of the valve member 15 which moves forward or rearward. As indicated by the characteristic curve (B), the frequency of the fan suddenly changes in a stepwise manner at a predetermined temperature, usually 60.degree. C. under normal operating conditions. Consequently, the amount of cooling air cannot be controlled adequately according to any great temperature change occurring while the vehicle is running. Hence, fan noise and power drain cannot be satisfactorily reduced. Also, the time taken to warm up the engine cannot be shortened sufficiently.